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Saturday, Apr 23, 2005

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Opinion - News Analysis

Antarctic glaciers receding: study

Aarti Dhar

244 glaciers studied Trend may be linked to climate changes Melt unlikely to raise sea levels

NEW DELHI: Almost all the glaciers that flow into the sea off the Antarctic Peninsula are receding. The discovery comes from an analysis spanning over half a century of aerial photographs and satellite images.

"Fifty years ago most glaciers were slowly growing in length, but the pattern is now reversed and these are shrinking," the British Antarctic Survey's Alison Cook said in London on Thursday.

Of the 244 glaciers studied, 87 per cent showed a net retreat since photographic evidence was first collected in the 1940s, according to Ms. Cook, who led the project.

The trend is probably linked to local climate changes on the peninsula where temperatures have risen by around 2ºC over the past 50 years. This is much more than the average temperature increase seen in the rest of the Antarctica, according to the findings of the study available on the online section of Nature magazine.

The researchers are not sure whether glaciers would be shrinking to the same extent across the rest of the continent. And they are also uncertain about the effects of the coastal glacier retreat. The ice blocks are typically about 2 km wide and several dozen km long. This is small compared to the peninsula's huge, floating ice shelves, which have likewise been disintegrating in recent years. The glacier melt is unlikely to raise sea levels much, or alter local salinity.

But if the glaciers retreat much further they may uncover bare rock, which could attract invasive species, the team says.

The survey, which is the most comprehensive of its kind so far, was completed by researchers from the Cambridge-based British Antarctic Survey and the U.S. Geological Survey, based in Virginia. Together, they scrutinised some 2,000 images to chart the changing positions of the mouths of the 244 glaciers. The study included glaciers that flow directly into the sea on a westerly stretch of the Antarctic Peninsula, which points up towards South America.

The study revealed that the mean rate of advance of glaciers in the 1940s and 1950s was slower than the current retreat. Widdowson Glacier, for example, has been receding by 1,100 metres each year for the past five years; in the 1940s it was advancing by just 200 metres annually.

Temperature is probably not the only cause. During the late 1980s there seems to have been a `blip,' during which the glaciers' retreat was curtailed even though temperatures continued to rise, probably because of changing ocean currents.

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